Re: Lockless page cache test results

[Jens Axboe <axboe@suse.de>]

On Thu, Apr 27 2006, Nick Piggin wrote:
> Jens Axboe wrote:
> 
> >Things look pretty bad for the lockless kernel though, Nick any idea
> >what is going on there? The splice change is pretty simple, see the top
> >three patches here:
> 
> Could just be the use of spin lock instead of read lock.
> 
> I don't think it would be hard to convert find_get_pages_contig
> to be lockless.

Ah, certainly, it's not lockless like find_get_page(). Care to do such a
patch?

> Patched vanilla numbers look nicer, but I'm curious as to why
> __do_page_cache was so bad before, if the file was in cache.
> Presumably it should not more than double tree_lock acquisition...
> it isn't getting called multiple times for each page, is it?

It still does a lot of extra work that's completely wasted. With
page_cache_readahead(), we should hit the RA_FLAG_INCACHE flag and be
done with it.

-- 
Jens Axboe